(p, n) Cross Section and Proton Optical-Model Parameters in the 4- to 5.5-Mev Energy Region

($p, n$) cross sections were measured for 18 medium-weight nuclei in the 4- to 5.5-Mev region. In this energy region, de-excitation of the compound nucleus by neutron emission is largely favored over charged particle emission; consequently, the ($p, n$) reaction dominates competing compound-elastic and inelastic scattering processes. The experimental results are compared with theoretical reaction cross sections predicted by the optical model for protons. It is found that the parameters which provide the best theoretical fit to these data also provide reasonable fits to neutron total, nonelastic, and elastic cross sections measured elsewhere when the latter are compared with theoretical cross sections predicted by the optical model for neutrons. It is concluded that the intrinsic nuclear well depth for protons and neutrons are equal to within ±7% uncertainty.